Resolving SINAMICS G110 F0072 USS Setpoint Fault on S7-1200 USS Networks

The SINAMICS G110 raises fault F0072 ("USS setpoint fault") when the drive stops receiving a valid process data setpoint over its RS485 USS port. On a network of three G110 inverters wired to a SIMATIC S7-1200 CPU, the fault typically trips all three drives simultaneously because every drive shares the same bus, the same master, and the same telegram timing. This reference walks through the firmware-level definition, parameter cross-check, root cause analysis, and step-by-step recovery using only parameters defined in the official G110 Operating Instructions.

1. F0072 - Definition and Drive Behavior

According to the G110 fault list, F0072 is the "USS setpoint fault." It is raised when the control unit has not received a fresh USS telegram within the telegram monitoring time defined in P2014. The drive reacts with the OFF2 stop command (pulse inhibit / coast-to-stop) by default, which is exactly the symptom reported: motors stop without a ramp. The companion fault F0085 ("External Fault") is sometimes stacked in the buffer when the same root cause is present.

Because the reaction is OFF2, the drive will not restart until F0072 is acknowledged, even if USS telegrams resume. This makes F0072 the most disruptive single fault on a small USS network.

2. Affected Products and Firmware

All G110 units from the 6SL3211 family share the same parameter set for USS, so the parameter addresses used below apply across the entire G110 range referenced in the 2009/2010 product phase.

3. USS Protocol Architecture Between S7-1200 and G110

USS is a master/slave serial protocol on RS485. The S7-1200 acts as the single master; each G110 is a slave addressed by P2011. Every G110 on the bus must be configured identically for telegram structure; the only thing that changes per node is the address.

Master (S7-1200 CPU)
   CB 1241 RS485 or CM 1241 RS485
        |  RS485 half-duplex, 2-wire
        +----- G110 #1   (P2011 = 1)
        +----- G110 #2   (P2011 = 2)
        +----- G110 #3   (P2011 = 3)
   Terminator ON at the two physical end nodes only

The TIA Portal instructions USS_PEZ_2 (drive sends back status) and USS_PEP_2 (drive only receives setpoint) sit on top of the CM/CB 1241 hardware. The USS background DB issues the USS_PORT calls that actually drive the serial port.

If the S7-1200 goes to STOP, USS_PORT stops driving the bus. Within P2014 milliseconds, every G110 raises F0072. This is the most common cause and is often mistaken for a wiring or baud problem.

4. Parameter Set Reported on the Field

The field report shows the following BOP-2 / IOP parameter set on the G110 drives. The third drive is configured for a different baud rate (9 = 57600 baud) while the other two run at 7 = 19200 baud.

The PZD/PKW length combination P2012 = 2 / P2013 = 4 is the standard "2-word setpoint + 4-word parameter channel" telegram used by the TIA Portal USS_PEZ_2 instruction. The length combination itself is correct.

5. Root Cause Analysis for the Reported Network

From the parameter dump and the symptom "all three drives trip together," four root causes have to be ruled out, in order of likelihood:

5.1 Baud rate mismatch on the third drive

Drive #3 is configured for 57600 baud while the S7-1200 and the other two drives are at 19200 baud. The S7-1200 USS_PORT drives the bus at a single baud. Drive #3 cannot decode telegrams, never returns a setpoint handshake, and the master may time out on the response window. Even though F0072 is generated by the drive when the drive itself does not see telegrams (a slave-side monitor), a stuck or misread bus can cascade the master's transmission schedule and starve the other two slaves. All three drives on a single USS segment must share the same baud rate.

5.2 S7-1200 going to STOP

If the CPU enters STOP (program error, OB not loaded, firmware download, etc.), USS_PORT stops. The drives see no telegram, and after P2014 = 300 ms every drive raises F0072. The fault will latch even when the CPU returns to RUN unless a fault-acknowledge path is configured.

5.3 Setpoint routed to PKW words instead of PZD

If the TIA Portal USS_PEZ_2 / USS_PEP_2 block is wired so that the speed setpoint is placed in the PKW channel of the telegram, the drive sees parameter writes (PKW) but no process setpoint (PZD). The drive interprets this as a "setpoint not present" condition and trips F0072. P1000 = 5 expects the setpoint on PZD word 1, not on the parameter channel.

5.4 Physical layer issues

Intermittent bus drops, missing terminating resistors at the two physical ends, swapped A/B wires (terminals 29 = P+ and 30 = N-), or a damaged CB/CB 1241 module will all look like F0072 because the drive cannot decode the incoming byte stream.

6. Required Checks Before Changing Any Parameter

1. Verify the baud rate index is identical on all three drives (P2010[0]). Pick one value, for example 7 = 19200, and write it to all three drives from the BOP or from the PLC.
2. Verify the USS node addresses are unique: P2011[0] = 1, 2, 3 with no overlap.
3. Confirm USS_PORT in TIA Portal is configured at the same baud as P2010 (e.g. 19200), with parity "No parity", flow control "None".
4. Check the S7-1200 CPU operating state (RUN / STOP / error LED). A CPU in STOP is the most common F0072 cause and the easiest to rule out.
5. Measure the RS485 bus with a scope at terminals 29/30 of the last drive. You should see 3-byte idle periods and the broadcast-style request from the master for every node.
6. Confirm terminating resistors are enabled only at the two physical ends. The G110 has a slide switch for the bus terminator; it must be ON at the two end nodes only.

7. Step-by-Step Resolution Procedure

7.1 Make all drives baud-rate-consistent

1. Set P2010[0] = 7 (19200) on all three drives. Save with the BOP "P" key.
2. Power-cycle each drive individually so the new baud takes effect.

7.2 Configure the S7-1200 USS master to match

1. In TIA Portal, open the USS_PORT instance DB. Set BAUD = 19200, PARITY = 0 (no parity), FLOW_CTRL = 0 (none), RESP_TO = 1000 (ms).
2. Make sure USS_PORT is called once per scan, ideally in OB1 (or a low-priority cyclic OB) with the EN input tied to a TRUE constant.
3. Wire a USS_PEZ_2 instance per drive. Use the STW (control word, e.g. 047Eh for run, 047Fh for run + enable setpoint) and SPD (speed setpoint in 0x4000-hex = 100%) inputs as the two PZD words out. The two PZD words back are the drive status word and actual speed.

7.3 Verify the setpoint is on PZD, not PKW

In the TIA Portal block instance, the input pins that go to the drive are:

• STW - control word, mapped to PZD word 1 (out)
• SP_EXT or SPEED_SP - main setpoint, mapped to PZD word 2 (out)

Do not write the setpoint into the parameter channel. With P2013 = 4 the PKW channel is present but the drive only uses it for parameter reads/writes; the running speed setpoint must be on PZD word 2.

7.4 Increase P2014 to absorb CPU start-up transients

P2014 is the maximum allowed telegram gap. With the value at 300 ms, any CPU restart or short glitch will trip F0072. Recommended values:

Set P2014[0] = 500 ms on every drive if you need the system to ride out a short CPU STOP transition.

7.5 Configure a fault-acknowledge path

1. Map a digital output from the S7-1200 to a G110 digital input that is wired to the fault-ack function. The G110 standard mapping is DI0 = 5 (fixed setpoint select) or DI1/DI2 = 9 (fault acknowledge), selectable via P0701-P0703.
2. Alternatively, send a rising edge on the control word bit 7 (fault acknowledge) on PZD word 1. The TIA Portal "USS_Drive" control DB has a dedicated ACK_FLT boolean input; drive it TRUE for one cycle after the drive returns to RUN.

7.6 Save parameters and power-cycle

1. Save the user parameter set to the EEPROM by setting P0971 = 1, or by long-pressing the BOP "P" key. This ensures the values survive a power loss.
2. Power-cycle the entire USS segment (drives + PLC).
3. Place the CPU in RUN. Watch the G110 BOP for F0072. The fault should not reappear after the first valid USS telegram.

8. Verification Procedure

After applying the changes, validate in this order:

1. Fault clears with no setpoint: With the CPU in RUN and USS_PORT active, force the drive's STW to 047Eh. The drive should enter "Ready to run" without re-tripping F0072.
2. Setpoint is accepted: Set SPEED_SP = 0x2000 (50%). The drive's actual speed output on PZD word 2 should ramp to 50% of P2000 reference. The G110 BOP should display a stable setpoint, not a flashing value.
3. CPU restart survival: Briefly stop the CPU (toggle the RUN/STOP switch or download a small program change). After the CPU returns to RUN, F0072 must not latch. If it does, P2014 is too low or the master is not configured for an auto-resend.
4. All three drives respond: Repeat steps 1-2 for slave addresses 1, 2, 3 by changing the SLAVE input of each USS_PEZ_2 instance. The BOP on each drive should show the same speed.
5. Long-run stability: Run the network for at least 30 minutes. Look at r0052 (drive state word) and confirm it stays in S2 (Operation enabled). Any F0072 entry in the fault buffer over that period indicates a residual bus quality problem.

9. Extended Diagnostics and Parameter Read-Back

If F0072 still occurs after the seven steps above, use the TIA Portal USS_Drive instruction (or the parameter channel) to read the following live values for deeper diagnosis:

The r2031[0] error counter is the most useful field counter. A non-zero value that climbs steadily points to electrical problems on the bus rather than a programming issue. A flat-zero error count combined with F0072 means the drive simply is not seeing any telegram - the master is at fault or the CPU is in STOP.

10. Preventive Measures for the Next Commissioning

• Document the baud, PZD/PKW length, and timeout per drive in the cabinet drawing.
• Add the fault-ack bit on the control word (PZD word 1, bit 7) to every PLC-to-drive telegram so F0072 can be cleared by software.
• Consider switching to USS_PEP_2 (no readback) if the S7-1200 is the only master and you do not need drive status. This halves the bus load and improves telegram timing margin.
• For larger or more critical systems, migrate to PROFINET with a SINAMICS G120C or V20 PN. The G110 has no PROFINET option, but the same F0072 logic and the same S7-1200 code patterns still apply to the G120 USS variant.

11. Troubleshooting Matrix

12. Frequently Asked Questions